Journal
NANO LETTERS
Volume 21, Issue 18, Pages 7887-7893Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.nanolett.1c00530
Keywords
Coherent phonons; dephasing; charge-carrier separation; electric field; bismuth oxyhalides; photocatalysis
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Funding
- Bavarian State Ministry of Science, Research, and Arts through the grant Solar Technologies go Hybrid (SolTech)
- Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany's Excellence Strategy-EXC [2089/1390776260]
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The study explores the potential of bismuth oxyiodide (BiOI) as a material for photocatalysis, highlighting coherent phonons induced by femtosecond laser pulse excitation. It identifies the presence of an electric field in BiOI along the [001] axis and its role in efficient charge separation, crucial for photocatalytic applications. Additionally, the research reveals two major dephasing mechanisms causing the loss of vibronic coherence in BiOI.
Bismuth oxyiodide (BiOI) is a promising material for photocatalysis combining intriguing optical and structural properties. We show that excitation by a femtosecond laser pulse creates coherent phonons inducing a time-variant oscillating modulation of the optical density. We find that the two underlying frequencies originate from lattice vibrations along the [001] crystallographic axis, the stacking direction of oppositely charged layers in BiOI. This is consistent with a subpicosecond charge separation driven by a built-in dipolar field. This partially screens the field, launching coherent phonons. Further, we determine the two major dephasing mechanisms that lead to the loss of vibronic coherence: (i) the anharmonic decay of an optical phonon into two acoustic phonons and (ii) phonon-carrier scattering. Our results provide a direct demonstration of the presence of an electric field in BiOI along the [001] axis and show its role in efficient charge separation that is crucial for photocatalytic applications of BiOI.
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